Each data point on each chart represents a different simulation, conducted at a different speed: 2.5 m/s (9km/h), 5.0 m/s (18 km/h) , 7.5 m/s (27 km/h), and 10 m/s (36 km/h). This should cover practically the full range of speeds observed in a typical Mini-Z track.

The curves were interpolated using a 2nd order polynomial. In all cases the fit was almost perfect (R-squared greater than 0.98) indicating that, according to the simulation, both drag and down forces increase as a proportion of speed squared. These results are pretty much in line with basic aerodynamics laws.